Methods and apparatuses for treatment of water are known in the art.
One such example is known from U.S. Pat. No. 3,170,868 which discloses a method and an apparatus for treating and agitating water in a reactor. The apparatus comprises means for adding a flocculation agent such that solids may be formed and separated in the reactor. The apparatus of U.S. Pat. No. 3,170,868 is controlled by determining the temperature upstream and downstream the reactor and determining the temperature difference upon which the agitation of the water is controlled. Alternatively, the system according to U.S. Pat. No. 3,170,868 is controlled on the basis of the turbidity of the water or the density of the water.
Further background art may be seen in U.S. Pat. No. 3,244,280, U.S. Pat. No. 4,670,142, U.S. Pat. No. 3,297,567, U.S. Pat. No. 5,616,831, U.S. Pat. No. 2,245,587 and U.S. Pat. No. 5,716,519.
It has been found that as conventional waste water treatment systems are operated in temperature ranges between 0 and 30 degrees Celsius, the density of water is substantially constant. This is illustrated in FIG. 11 and described in the description relating thereto.
Moreover it has been found that the turbidity of water is primarily determined by the level of organic material in the water (up to 99 percent of the turbidity being created by organic material) and not the level of sand/grit in the water.
Furthermore, it has been found that in waste water treatment systems the difference in temperature between a point upstream the sedimentation chamber and a point downstream the sedimentation chamber is insignificant. Most surprisingly it has been found to be the case for all temperatures of the year. Accordingly, no or little natural convection occurs in such chambers, as the waste water flowing into the chamber has substantially the same temperature as the water which flows out of the chamber. It has been found that for normal operating temperature (0-30 degrees Celsius) of the waste water, the difference between the temperature of water flowing into and out of the chamber is less than 0.1 degree Celsius.
In order to separate sand and/or grit from waste water, waste water treatment plants often comprise a grit chamber. During operation sand and grit containing waste water flows into the grit chamber which is designed to allow the sand and grit to settle at the bottom/floor of the chamber. In order to ensure that sand/grit particles larger than a predetermined size settles on the floor of the grit chamber, and that particles such as sand, grit and organic particles, smaller than the predetermined size are allowed to leave the grit chamber by being suspended in the waste water, grit chambers may comprise diffusers for increasing the turbulence in the waste water.
However a certain degree of turbulence is needed in order to prevent most of the organic material from settling in the grit chamber, while allowing sand/grit to settle.
Accordingly, it is an object of a preferred embodiment of the present invention, to provide a system for controlling the sedimentation of sand and/or grit particles in a grit chamber.
Especially, it is an object of a preferred embodiment of the present invention to provide a system wherein as much organic material is transported through the grit chamber while as much sand and grit is allowed to settle in the grid chamber.
Moreover it is an object of a preferred embodiment of the present invention, to provide a system which is adapted to maintain substantially the same level of sedimentation for a predetermined period of time such as at least one year or such as at least one season during which the temperature varies.
Moreover, it is an object of a preferred embodiment of the present invention to provide a system wherein the amount of sand in the subsequent process tanks is reduced.
It is an object of a preferred embodiment of the present invention to provide a system which is adapted to allow as much organic material to pass though the system as possible for a given sedimentation threshold i.e. for a given maximum size of the largest particle allowed to be transported through the chamber/reservoir.
Furthermore, it is an object of a preferred embodiment of the present invention to provide a system wherein tear and wear of e.g. pipes and pumps is reduced. Moreover, it is an object of a preferred embodiment of the present invention to provide a system wherein the capacity of process tanks subsequent to the grit chamber is increased.
Additionally, it is an object of a preferred embodiment to provide a grit chamber wherein the turbulence created by means of the diffusers is more uniform along the length of the grit chamber. Furthermore, it is an object of an embodiment of the present invention to reduce power consumption of grit chambers with turbulence creating means.